When you are in a subgroup, to return to the main group you have to go up to "Your Groups" in the header and click on the group from there. For those who are reading this in the Beta group, this is not big deal...we have always done it this way. But if you are a not-so-savvy new member of a group, it is a path that is not obvious. When you are in the main group all navigation is from the tab bar on the left, and then all of a sudden you have to go up in the header. This is not a hypothetical point of confusion, I'm dealing with it right now with new users.
I have a suggestion which I believe will help in the overall user-friendliness of the site. It involved 2 changes:
1 - "stick" a tab at the top called "Main Home" which will always be there and take folks to the main group's home page.
2 - Indent the tabs for the subgroup.
It would look like this:
I believe this would go a long way in making the site navigation, especially for the new user, much more intuitive.